The goal of this project is to identify mechanisms mediating effects of endogenous TGF-b1 on the development and function of specific hematopoietic cell lineages. Experimental evidence from in vitro studies of function suggest a critical role for TGF-b1 in regulating myelopoiesis and immune cell function, but such studies are limited by their inability to reproduce the complex in vivo network which ordinarily influences the genesis and function of these cell populations. Our approach to this problem has been to utilize the TGF- b1(-/-) mouse as the basis for establishing complimentary in vivo model systems, each designed to isolate TGF-b1 deficiency in a background that allows for determination of the significant growth-inhibitory and tumor suppressor functions of the molecule in the adult mouse. This approach has enabled us to identify critical links between cell cycle control by TGF-b1, immune cell maturation and function, and hematopoietic cell growth and differentiation, as they occur in vivo. Examples include our demonstration of myeloid hyperplasia as a distinct phenotype in TGF-b1(- /-) mice, and of the contributions of several regulators of the cell cycle to the establishment of the autoimmune process which evolves in the absence of endogenous TGF-b1. Through adoptive transfer studies, including bone marrow transplant experiments and studies of thymic and splenic reconstitution in nude mice, we have also identified novel autocrine effects of TGF-b1 and their role in the autoimmune and hematopoietic manifestations of TGF-b1 deficiency. Through collaboration with the Dermatology Branch in the DCS, we have determined that TGF-b1(- /-) mice lack epidermal Langerhans cells (LC) and gp40 positive dendritic cells (DC) in lymph nodes, suggesting that lymphoid DC as well as LC are perturbed. We aim to study DC populations in TGF-b1(-/-) mice, including MHC-II(-/-) and athymic nude strains developed in our lab, and to determine precise mechanisms by which TGF-b1 regulates development of both lymphoid and myeloid lineages. Our primary goal is to define the cellular and molecular events which mediate these effects, paricularly those that govern cell cycle progression and the growth inhibitory responses to TGF-b.